1. Field of the Invention
The present invention relates to an image processing apparatus that is capable of combining a copy-forgery-inhibited pattern image and an original image so as to output a combined image, and to a method of controlling the information processing apparatus.
2. Description of the Related Art
There are special sheets called forgery-inhibited sheets or security paper. In a forgery-inhibited sheet, a string of characters, such as “COPY”, is invisibly hidden at a glance. However, the hidden string of characters appears on a copy of the forgery-inhibited sheet. Thus, a document produced using such a forgery-inhibited sheet, can easily be discerned from its copy. Also, to use a copy of such document can cause hesitation.
Forgery-inhibited sheets have the above advantages. Therefore, forgery-inhibited sheets have been utilized to make ledger sheets, resident cards, and so on. However, forgery-inhibited sheets have drawbacks in that they are high in price, as compared with sheets of plain paper, and that only strings of characters hidden in the forgery-inhibited sheet at the time of its production can appear on a copy sheet.
In view of the above mentioned drawbacks associated with forgery-inhibited sheets, in recent years, a new technique having advantages similar to those of forgery-inhibited sheets has attracted attention. According to this technique, document data and copy-forgery-inhibited pattern (also referred to as copy-inhibited pattern) image data generated by a computer are synthesized in a printer, and the pattern-containing-image data obtained by this synthesis is output to a sheet of standard paper. A string of characters, or the like is hidden in this copy-forgery-inhibited pattern image. Thus, the hidden string of characters appears on a copy of the pattern-containing-image, similar to the case of using a forgery-inhibited sheet. Additionally, since this technique utilizes a sheet of standard paper, this technique has an advantage in that an original can be produced inexpensively, as compared with the case of utilizing a forgery-inhibited sheet. Also, according to this technique, new copy-forgery-inhibited pattern image data can be generated every time an original document is produced. Thus, this technique has another advantage in that the color of a copy-forgery-inhibited pattern image and a hidden string of characters can be freely set.
Meanwhile, this copy-forgery-inhibited pattern image includes an area in which an image “remains (appears)” on the copy, and an area in which an image “disappears” on the copy (or the density of this area is lower, as compared with the former area). These two areas have substantially the same reflection density on the original. Thus, the human eye cannot recognize that a string of characters, such as “COPY”, is hidden in the original. The word “remain” means that an image on an original is exactly reproduced on a copy. Further, the word “disappear” means that an image on an original is not reproduced on a copy. The reflection density is measured by a reflection densitometer.
Hereinafter, the area, in which an image “remains” on the copy, is referred to as a “latent image area”. The area, in which an image “disappears” on the copy (or the density of this area is lower, as compared with the former area), is referred to as a “background area”.
FIG. 19 is a view showing an arrangement of dots in a copy-forgery-inhibited pattern image. In FIG. 19, an area in which dots are arranged in a concentrated manner, is a latent image area. An area in which dots are arranged in a dispersed manner, is a background area. Dots shown on each of the two areas are formed by different halftone dot processes or different dithering processes. For example, the dots of the latent image area are formed by a low resolution screen processing. The dots of the background area are formed by a high resolution screen processing. Alternatively, the dots of the latent image area are formed using a dot-concentrated-type dither matrix. The dots of the background area are formed using a dot-dispersed-type dither matrix.
Meanwhile, the reproduction ability of a copying machine depends on the input resolution and the output resolution of the copying machine. Thus, there is a limit to the reproduction ability of the copying machine. Consequently, in the case where the dots of the latent image area of the copy-forgery-inhibited pattern image are larger than dots that can be reproduced by a copying machine, and where the dots of the background area of the copy-forgery-inhibited pattern image are smaller than dots that can be reproduced by the copying machine, the dots of the latent image area on a copy can be reproduced, however the dots of the background area are difficult to reproduce. As a result, the latent image area is densely reproduced on the copy in comparison with the background area. Hereinafter, a phenomenon is called “visualization” in which a hidden string of characters appears just as floating on a copy because the latent image area is densely reproduced in comparison with the background area.
FIGS. 20A and 20B are views illustrating this “visualization”. FIGS. 20A and 20B conceptually illustrate that concentrated dots (large dots) are reproduced on a copy, and that dispersed dots (small dots) are not exactly reproduced thereon.
The configuration of the copy-forgery-inhibited pattern image is not limited to the aforementioned configuration. It is sufficient that strings of characters recognizable to the human eyes, such as “COPY”, symbols, or patterns appear (or are visualized) on a copy. Also in the case where the string of white characters, such as “COPY” is shown on a colored area, this copy-forgery-inhibited pattern image substantially achieves its purpose. In this case, the region of the characters “COPY” is called the “background area”.
As described above, a technique for making the latent image less visible has been developed. In addition, Japanese Patent Application Laid-Open No. 2005-151456 discusses a technique in which large and small dots are disposed in the latent image area in a mixed manner in order to make the latent image less visible on the original. In this technique, the latent image area is divided into plural regions. Disposition of the dots is controlled such that the dots to be reproduced at the time of copying are disposed in at least one region among the plural regions, and the dots are not disposed in at least one region other than the region in which the dots are disposed. In this way, the latent image is less visible in the original, compared to the conventional technology in which only the large dots are disposed in the latent image area.
As described above, the technique in which large and small dots are disposed in the latent image area in a mixed manner has been developed, however, an environment such as a user interface (UI) for utilizing the technique is not well established yet. For example, according to the technique that Japanese Patent Application Laid-Open No. 2005-151456 discusses, large and small dots are disposed in the latent image in a mixed manner. Consequently, invisibility of the latent image on the original is improved, however, an effect of visualization of the latent image on the copy is reduced, as compared to the technique in which only the large dots are disposed in the latent image area. In order to allow a user to select a desirable technique while the user can recognize the disadvantage described above, an environment for utilizing the technique such as the UI needs to be established. In addition, in order to allow the user to readily change a ratio of large and small dots, also the environment for utilizing the technique such as the UI needs to be established